1. Field of the Invention
The present invention relates to a mat, a method for producing the mat, and an exhaust gas purifying apparatus.
2. Discussion of the Background
Conventionally known mats include nonwoven fabric-like mats made from compressed inorganic fibrous materials such as fibrous silica or fibrous alumina. These mats are excellent in characteristics such as heat resistance and elasticity (repulsive force), and thus they are used for various applications.
For example, such a mat is used as a component of an exhaust gas purifying apparatus.
Specifically, a typical exhaust gas purifying apparatus includes a cylindrical exhaust gas treating body, a cylindrical casing which accommodates the exhaust gas treating body, and a mat-shaped holding sealing material disposed between the exhaust gas treating body and the casing, and the mat is used as a material for this holding sealing material. The holding sealing material is produced through steps such as a step of cutting a mat into a predetermined shape.
The holding sealing material which includes a nonwoven fabric-like mat having repulsive force has a predetermined holding force. Thus, in the exhaust gas purifying apparatus, the holding sealing material securely holds the exhaust gas treating body at a predetermined position inside the casing. Further, since the holding sealing material is disposed between the exhaust gas treating body and the casing, the exhaust gas treating body is less likely to be in contact with the casing even if vibration or the like is applied, and exhaust gas is less likely to leak from between the exhaust gas treating body and the casing.
The exhaust gas purifying apparatus including a holding sealing material may be produced by stuffing an exhaust gas treating body wrapped with a holding sealing material into a casing.
Specifically, a holding sealing material is wrapped around the periphery of a cylindrical exhaust gas treating body to prepare a wrapped member, and the wrapped member is slide-stuffed into a cylindrical casing whose inner diameter is smaller than the outer diameter of the wrapped member while the holding sealing material is compressed.
In this production method, therefore, the holding sealing material wrapped around the exhaust gas treating body is required to have an appropriately low volume so that the wrapped member is easily stuffed.
Further, a high shearing force is applied to the holding sealing material when the holding sealing material is stuffed into the casing. Thus, the holding sealing material is required to have a certain degree of strength (hereinafter, also referred to simply as shear strength) so as not to be torn due to the shearing force.
Furthermore, the holding sealing material is required to have a certain degree of flexibility so as not to suffer crackings when wrapped around the exhaust gas treating body.
JP-A 62-56348 discloses a conventional mat including fibrous alumina as a mat for such a holding sealing material.
This conventional mat is produced as follows: a fibrous alumina precursor, which is to be converted into an inorganic fibrous substance by firing, is compressed to prepare a sheet; multiple needles with barbs are inserted into/extracted from the sheet along the thickness direction of the sheet to prepare a needled sheet with intertwined portions formed therein; and the needled sheet is fired.
The produced mat is cut into a predetermined shape, and thereby a holding sealing material is produced.
JP-A 59-519 discloses a conventional mat produced by preparing a sheet-formed sheet including an inorganic fibrous substance, stacking a polyester-fiber nonwoven fabric on the upper face of the sheet, and needling the sheet in a manner as mentioned above.
The produced mat is cut into a predetermined shape, and thereby a holding sealing material is produced.
The contents of JP-A 62-56348 and JP-A 59-519 are incorporated herein by reference in their entirety.